In internal combustion engines, variable valve controllers are used in order, on one hand, to use the available engine power as effectively as possible with respect to the development of rotational speed-dependent power and torque and, on the other hand, to adjust the idling behavior and also the fuel consumption and the exhaust-gas emissions to a favorable or low setting. This is possible by varying the valve control times and valve strokes of the gas-exchange valves or through timed deactivation of individual gas-exchange valves or entire cylinders. In particular, for internal combustion engines with many cylinders and valves, through a complete shutdown of several valves or one or more cylinders, in a partial load mode and also during idling, considerable fuel savings and a reduction in pollutant emissions can be achieved. For this purpose, for one, a switchable cam follower, i.e., switchable tappet, rocker arm, or valve lifter can be used, wherein the associated switching mechanisms are formed either in conventional ways on the cam follower or, as described, for example, in the unpublished Patent Application Nos. DE 10 2007 031 815.6 and DE 2007 040 021.9 of the applicant, are shifted at least partially toward the camshaft. Second, adjustable camshafts and also camshaft arrangements can be used with cams that can be adjusted relative to the camshaft.
For the design and implementation of a variable valve train in a vehicle, the requirements for installation space of the switchable valve train components are gaining more and more significance, because reduced space conditions are given in modern engines with typically four valves per cylinder. The problem of installation space is heightened even more by the increasing use of direct fuel-injection systems. In addition, the required switching forces for the adjustment of the valve train and for the activation of the gas-exchange valves should be as small as possible, in order to keep the wear in the valve train low. Here, a shifting of the switching function to the camshaft has proven favorable.
In U.S. Pat. No. 5,239,885, a known camshaft arrangement is described in which a rotationally fixed connection between a camshaft and a cam arranged on the camshaft fixed in the axial direction can be established and released selectively by a coupling device. The coupling device has a coupling pin extending into a radial borehole of the camshaft and loaded with a compression spring. This coupling pin is supported by the spring force in the radial direction in a recess within the cam, so that the cam is locked in rotation. Here, the coupling pin sits with a positive fit in a conical receptacle region formed in the recess. In continuation of the coupling recess, a pressure chamber is formed that can be set under pressure with a hydraulic medium by an axial pressurized medium feed to the camshaft and a connection channel.
For unlocking the cam, in the pressure chamber an oil pressure is established that acts against the spring force, by which the coupling pin is forced back as far from the recess into the camshaft borehole until relative movements between the camshaft and the cam are possible that are applied when the cam elevated section reaches the allocated cam follower during the camshaft rotation. The allocated cam follower is thus not loaded with an adjustment force, so that, as a consequence, the corresponding gas-exchange valve is not opened.
This publication further proposes, for simplifying the mechanical configuration and the processing of the cam arrangement, an inclination of the coupling relative to the camshaft axis, by which an otherwise required ventilation borehole with a closure piece in the cam reference circle is eliminated. Instead, on the reference circle of the cam there is a recess reducing its width for a simplified introduction of the coupling pin into the configuration. In addition, the compression spring is eliminated. For producing the locking position, instead, the pin is loaded hydraulically by a front-end pressure chamber and the previous pressure chamber is provided with a ventilation borehole. An unlocking position is achieved by centrifugal forces during the camshaft rotation when the hydraulic loading is eliminated and optionally secured by additional measures. Because the receptacle surfaces of the coupling pin and the recess absorb the activation forces during locking and, in the locking position, all of the relative forces generated between the cam and the camshaft, the locking arrangement is relatively susceptible to wear or requires, for a long-lasting, trouble-free function, at least relatively high manufacturing expense with small production tolerances.
Furthermore, for example, from U.S. Pat. Nos. 5,158,049, 5,645,022, US 2007/0034184, and U.S. Pat. No. 7,114,473 (DE 10 2004 036 764 A1), valve trains are known in which cams are arranged so that they can move in the axial direction on a camshaft. Through the use of different mechanisms and controls described in the noted publications, through the axial shifting of at least one cam, gas-exchange valves can be deactivated and/or loaded with different valve strokes. Such axial shifting devices indeed offer, in principle, an array of adjustment options, in particular, also with a section of several cam tracks. However, they require a relative large axial structural width that, as already mentioned, is often not available in modern internal combustion engines or that requires at least complicated structural changes to the internal combustion engine.